使用ObservableCollection的Windows Phone 8.1 WinRT内存泄漏

Question

我正在使用大量的对象(PO​​I)来显示MapControl.我正在帮助自己使用MVVM Light来遵守MVVM方法的规则.

由于我有义务在地图上显示每个对象,我必须使用MapItemsControl集合,而不是MapElements一个.此集合绑定到对应的ObservableCollection<PushpinViewModel>object(Pushpins)ViewModel.当我想要刷新时,一切都按预期工作,直到现在Pushpins.问题是内存泄漏.但首先,一些代码可视化问题:

XAML:

<maps:MapControl x:Name="Map"
                 x:Uid="MapControl">
  <maps:MapItemsControl ItemsSource="{Binding Pushpins}">
    <maps:MapItemsControl.ItemTemplate>
      <DataTemplate>
        <Image Source="{Binding Image}"/>
      </DataTemplate>
    </maps:MapItemsControl.ItemTemplate>
  </maps:MapItemsControl>

MainViewModel:

public class MainViewModel : ViewModelBase
{
    public RelayCommand AddCommand { get; set; }
    public RelayCommand ClearCommand { get; set; }
    public RelayCommand CollectCommand { get; set; }

    public ObservableCollection<PushpinViewModel> Pushpins { get; set; }

    /* Ctor, initialization of Pushpins and stuff like that */

    private void Collect()
    {
        GC.Collect(2);
        GC.WaitForPendingFinalizers();
        GC.Collect(2);
        PrintCurrentMemory();
    }

    private void Clear()
    {
        Pushpins.Clear();
        PrintCurrentMemory();
    }

    private void Add()
    {
        for (int i = 0; i < 1000; i++)
        {
            Pushpins.Add(new PushpinViewModel());
        }
        PrintCurrentMemory();
    }

    private void PrintCurrentMemory()
    {
        Logger.Log(String.Format("Total Memory: {0}", GC.GetTotalMemory(true) / 1024.0));
    }
}

PushpinViewModel:

public class PushpinViewModel: ViewModelBase
{
    public string Image { get { return "/Assets/SomeImage.png"; } }

    ~PushpinViewModel()
    {
        Logger.Log("This finalizer never gets called!");
    }
}

现在,请考虑以下方案.我添加了Pushpins1000个PushpinViewModel元素的集合.它们被渲染,内存被分配,一切都很好.现在我想清除集合,并添加另一个(在真实场景中不同)1000个元素.所以,我称之为Clear()方法.但是......没有任何反应!Pushpins被清除了,但是PushpinViewModel终结者没有被召唤!然后我再次添加1000个元素,我的内存使用量翻倍.你可以猜到接下来会发生什么.当我重复这个Clear()- Add()程序3-5次我的应用程序崩溃.

那么,问题是什么？显然ObservableCollection是在PushpinViewModel对象Clear()上执行之后保持对对象的引用,因此它们不能被垃圾收集.当然,强制GC执行垃圾收集并没有帮助(有时甚至会使情况变得更糟).

现在困扰我2天了,我尝试了许多不同的场景来尝试克服这个问题,但说实话,没有任何帮助.只有一件事毫无价值 - 我不记得确切的情况,但是当我分配Pushpins = null,然后做了更多的事情时,VehiceViewModel它们被摧毁了.但这对我不起作用,因为我还记得我在地图上显示这些图钉后出现问题Clear().

你有什么想法会导致这种内存泄漏吗？我如何强迫OC成员摧毁？也许有某种替代方案OC？在此先感谢您的帮助!

编辑:

我使用XAML Map Control进行了一些测试 - https://xamlmapcontrol.codeplex.com/,结果令人惊讶.添加了> 1000个元素的整体地图性能比本机更差MapControl,但是,如果我调用Add()x1000,那么Clear(),然后Add()x1000,这个PushpinViewModel终结器正在调用!内存被释放,应用程序不会崩溃.所以微软肯定有问题MapControl......

Answer 1

好的,这是我模仿的行为MapItemsControl.请注意,这是非常未经测试的 - 它适用于我的应用程序,但实际上并没有在其他任何地方尝试过.我从来没有测试过这个RemoveItems功能,因为我的应用只是添加了一个项目ObservableCollection并清除它们; 它永远不会逐步删除项目.

另请注意,它使用绑定的项的哈希码标记XAML图钉; 这是它如何识别集合更改时从地图中删除哪些图钉.这可能不适用于您的情况,但似乎是有效的.

用法:

注意:NumberedCircle用户控件只是一个红色圆圈,在其中显示一个数字; 替换为您想要用作图钉的任何XAML控件.Destinations是我ObservableCollection的对象有一个Number属性(显示在图钉内)和一个Point属性(图钉位置).

<map:MapControl>
   <i:Interaction.Behaviors>
      <behaviors:PushpinCollectionBehavior ItemsSource="{Binding Path=Destinations}">
         <behaviors:PushpinCollectionBehavior.ItemTemplate>
            <DataTemplate>
               <controls:NumberedCircle Number="{Binding Path=Number}" map:MapControl.Location="{Binding Path=Point}" />
            </DataTemplate>
         </behaviors:PushpinCollectionBehavior.ItemTemplate>
      </behaviors:PushpinCollectionBehavior>
   </i:Interaction.Behaviors>
</map:MapControl>

码:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Microsoft.Xaml.Interactivity;

using Windows.Devices.Geolocation;
using Windows.Foundation;
using Windows.Storage.Streams;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls.Maps;

namespace Foo.Behaviors
{
    /// <summary>
    /// Behavior to draw pushpins on a map.  This effectively replaces MapItemsControl, which is flaky as hell.
    /// </summary>
    public class PushpinCollectionBehavior : DependencyObject, IBehavior
    {
        #region IBehavior

        public DependencyObject AssociatedObject { get; private set; }

        public void Attach(Windows.UI.Xaml.DependencyObject associatedObject)
        {
            var mapControl = associatedObject as MapControl;

            if (mapControl == null)
                throw new ArgumentException("PushpinCollectionBehavior can be attached only to MapControl");

            AssociatedObject = associatedObject;

            mapControl.Unloaded += MapControlUnloaded;
        }

        public void Detach()
        {
            var mapControl = AssociatedObject as MapControl;

            if (mapControl != null)
                mapControl.Unloaded -= MapControlUnloaded;
        }

        #endregion

        #region Dependency Properties

        /// <summary>
        /// The dependency property of the item that contains the pushpin locations.
        /// </summary>
        public static readonly DependencyProperty ItemsSourceProperty =
            DependencyProperty.Register("ItemsSource", typeof(object), typeof(PushpinCollectionBehavior), new PropertyMetadata(null, OnItemsSourcePropertyChanged));

        /// <summary>
        /// The item that contains the pushpin locations.
        /// </summary>
        public object ItemsSource
        {
            get { return GetValue(ItemsSourceProperty); }
            set { SetValue(ItemsSourceProperty, value); }
        }

        /// <summary>
        /// Adds, moves, or removes the pushpin when the item source changes.
        /// </summary>
        private static void OnItemsSourcePropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
        {
            var behavior = dependencyObject as PushpinCollectionBehavior;
            var mapControl = behavior.AssociatedObject as MapControl;

            // add the items

            if (behavior.ItemsSource is IList)
                behavior.AddItems(behavior.ItemsSource as IList);
            else
                throw new Exception("PushpinCollectionBehavior needs an IList as the items source.");

            // subscribe to changes in the collection

            if (behavior.ItemsSource is INotifyCollectionChanged)
            {
                var items = behavior.ItemsSource as INotifyCollectionChanged;
                items.CollectionChanged += behavior.CollectionChanged;
            }
        }

        // <summary>
        /// The dependency property of the pushpin template.
        /// </summary>
        public static readonly DependencyProperty ItemTemplateProperty =
            DependencyProperty.Register("ItemTemplate", typeof(DataTemplate), typeof(PushpinCollectionBehavior), new PropertyMetadata(null));

        /// <summary>
        /// The pushpin template.
        /// </summary>
        public DataTemplate ItemTemplate
        {
            get { return (DataTemplate)GetValue(ItemTemplateProperty); }
            set { SetValue(ItemTemplateProperty, value); }
        }

        #endregion

        #region Events

        /// <summary>
        /// Adds or removes the items on the map.
        /// </summary>
        private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Add:
                    AddItems(e.NewItems);
                    break;

                case NotifyCollectionChangedAction.Remove:
                    RemoveItems(e.OldItems);
                    break;

                case NotifyCollectionChangedAction.Reset:
                    ClearItems();
                    break;
            }
        }

        /// <summary>
        /// Removes the CollectionChanged event handler from the ItemsSource when the map is unloaded.
        /// </summary>
        void MapControlUnloaded(object sender, RoutedEventArgs e)
        {
            var items = ItemsSource as INotifyCollectionChanged;

            if (items != null)
                items.CollectionChanged -= CollectionChanged;
        }

        #endregion

        #region Private Functions

        /// <summary>
        /// Adds items to the map.
        /// </summary> 
        private void AddItems(IList items)
        {
            var mapControl = AssociatedObject as MapControl;

            foreach (var item in items)
            {
                var templateInstance = ItemTemplate.LoadContent() as FrameworkElement;

                var hashCode = item.GetHashCode();

                templateInstance.Tag = hashCode;
                templateInstance.DataContext = item;

                mapControl.Children.Add(templateInstance);

                Tags.Add(hashCode);
            }
        }

        /// <summary>
        /// Removes items from the map.
        /// </summary>
        private void RemoveItems(IList items)
        {
            var mapControl = AssociatedObject as MapControl;

            foreach (var item in items)
            {
                var hashCode = item.GetHashCode();

                foreach (var child in mapControl.Children.Where(c => c is FrameworkElement))
                {
                    var frameworkElement = child as FrameworkElement;

                    if (hashCode.Equals(frameworkElement.Tag))
                    {
                        mapControl.Children.Remove(frameworkElement);
                        continue;
                    }
                }

                Tags.Remove(hashCode);
            }
        }

        /// <summary>
        /// Clears items from the map.
        /// </summary>
        private void ClearItems()
        {
            var mapControl = AssociatedObject as MapControl;

            foreach (var tag in Tags)
            {
                foreach (var child in mapControl.Children.Where(c => c is FrameworkElement))
                {
                    var frameworkElement = child as FrameworkElement;

                    if (tag.Equals(frameworkElement.Tag))
                    {
                        mapControl.Children.Remove(frameworkElement);
                        continue;
                    }
                }
            }

            Tags.Clear();
        }

        #endregion

        #region Private Properties

        /// <summary>
        /// The object tags of the items this behavior has placed on the map.
        /// </summary>
        private List<int> Tags
        {
            get
            {
                if (_tags == null)
                    _tags = new List<int>();

                return _tags;
            }
        }
        private List<int> _tags;

        #endregion
    }
}